I broke in the barrel with 1 shot / clean for the first 10 rounds. Then 3-shot groups (beginning load development) - clean. Once I'd shot 30 rounds, I shot 5 shot groups (continuing load development) - clean. From about 50 til now (just over 200) I clean after ever 10 - 15 rounds (carbon and copper everytime). I've tried to concentrate on neck sized brass / win 780 supreme loads adjusting seating depth and powder amount and just don't have any consistency. A few times, I've gone back to some other powders that shot well with new brass (7828ssc & H1000). Both of these powders shot sub-moa with new brass and now will not group.
The only other difference since I started is the weather has warmed 20 - 25 degrees. Maybe 780 supreme is temp sensitive?
I don't think it's shooting form, bench practices, etc. Just to make sure, I shot 3 other rifles from the same set up. All were around .5 moa at 100 yards.
I do run one oil patch down the bore (followed by a dry) after cleaning carbon and copper. I've heard some folks say it takes a dozen rounds to burn out oil - others swear by running an oil patch through???? Doesn't seem to make a difference in my other rifles.
The rifle is a stainless cdl in 264 win mag. I put on a Bell and Carlson Medalist stock (with aluminum bedding block), and a VX3 6.5-20x50 LRT with talley one piece rings. Last night I checked all action screws and scope mount screws again.
Maybe I just need to work up different loads now that the barrel is broke in instead of trying to force another 0.34 group with 780? I've got a bedding kit ordered. I guess the next order of business is bolt trueing?